If the house is on a private well and the air test is elevated, it is worth testing the water too. The EPA says soil gas is usually the much bigger risk, and most water risk comes from radon released into the air by showers and laundry.
More detail
Private wells are common on the rural edges of the service area, around Granville, Johnstown, Galena, Sunbury, Marysville, and Plain City. Ohio's private water rules in OAC 3701-28 cover well construction, permits, and sampling through local boards of health but set no radon limit, so a well is never checked for radon unless the owner asks. Public water drawn from rivers and reservoirs is not usually a radon concern, and a public system that uses groundwater can answer questions about its own supply. If a water result comes back high, point-of-entry treatment covers the whole house: the EPA rates aeration at 95 to 99 percent removal and granular activated carbon at 85 to 95 percent for moderate levels, with by-products building up in the carbon. See radon in private wells.